The present invention pertains to well pump rod, including a rod commonly known as a sinkerbar, which is provided with a high density polyethylene sleeve disposed thereover to minimize wear on the rod and well tubing in which it is disposed. The invention also pertains to preferred methods and apparatus for applying a polyethylene sleeve to a pump rod or xe2x80x9csinkerbarxe2x80x9d.
Downhole well pumps which utilize elongated strings of so-called xe2x80x9csucker rodsxe2x80x9d as the pump actuating mechanism are widely used for various well pumping applications. Although it was once and long-considered a suitable design to provide a pump rod string, with rod sections having the smallest diameter disposed in the string directly above the pump, with progressively increasing rod diameters in the rod string near the earth""s surface, this configuration produces a tendency to significantly buckle and bend the rod string at the rod sections of smallest diameter, that is just above the pump, and cause substantial abrasion of the rod string as well as the tubing string in which the rod and pump are disposed. Consequently, more recent design techniques have utilized rod sections of larger diameter near the bottom of the rod string and directly above the pump, and commonly known as xe2x80x9csinkerbarsxe2x80x9d.
By way of example, a pump rod string including 1.50 inch diameter sinkerbars connected end to end in the bottom 300 feet to 500 feet of the string, directly above the pump, allows the rod string to maintain tension and allows the highest compressive or buckling forces to occur in the relatively larger diameter sinkerbar sections. Accordingly, sinkerbar sections having a larger diameter, compared to the rest of the rod string, are less likely to buckle in compression and when elastic deflection of the sinkerbars occurs and the well tubing is engaged thereby, the contact is disposed over a greater surface area and tends to reduce wear which ultimately requires replacement of the rod and/or the tubing string.
Even with the development of larger diameter rod sections or so-called sinkerbars, there have been efforts to reduce wear on the tubing string by providing, for example, a high or ultra-high density polyethylene liner inside the tubing string, which minimizes wear and friction caused by engagement with a deflected pump rod string. However, certain drawbacks are associated with this approach to reducing wear on tubing as well as rod strings, namely, a reduction in the effective inside diameter of the tubing string due to the thickness of the polyethylene liner and the requirement to install substantial lengths, up to several thousand feet, of lined tubing string in the well in order to accommodate the entire length of pump rod string which is likely to be deflected into engagement with the tubing string as a result, for example, of changing the position of the pump within the tubing string from time to time. U.S. Pat. No. 5,511,619 issued to William E. Jackson on Apr. 30, 1996 describes an example of the aforementioned approach. However, the present invention contemplates an alternative, improved solution to the problems associated with rod actuated well pumps, as discussed hereinabove.
The present invention provides an improved elongated pump rod section or sinkerbar for use with downhole rod actuated well pumps and the like.
In accordance with one aspect of the invention, an elongated pump rod or xe2x80x9csinkerbarxe2x80x9d is provided which includes a sleeve of polymer material disposed over a major portion of the exterior of the rod or sinkerbar and preferably comprises polyethylene, high density polyethylene or ultra high density polyethylene. This sleeve provides a bearing surface which reduces friction and wear on the well tubing and the pump rod or sinkerbar in the event of engagement between the sinkerbar and the well tubing.
By placing a sleeve of polymer material, such as polyethylene, on the exterior of the pump rod or sinkerbar and in accordance with methods contemplated by the invention, there is no requirement to utilize non-standard tubing string sizes, and/or limit well fluid flow resulting from a reduced internal diameter of the tubing string. At the same time, the ability to maintain tension in the pump rod string and reduce wear on the pump rod string and the tubing string is provided. Moreover, by utilizing only a few hundred feet (200 feet to 500 feet) of pump rod or sinkerbar string incorporating the polyethylene or other polymer sleeve thereover, the cost of providing a wear-reducing arrangement for rod actuated well pumps is reduced.
The present invention also contemplates the provision of methods and apparatus for applying a polymer sleeve over a substantially cylindrical elongated section of a pump rod or sinkerbar. One embodiment of the method and apparatus utilizes a hydraulic cylinder which is operable to engage one end of the rod or sinkerbar and forcibly displace it within a section of stationary polyethylene tubing. Another embodiment contemplates a method and apparatus which holds the rod or sinkerbar stationary and utilizes a hydraulic cylinder actuator to forcibly displace the polyethylene sleeve over the outer diameter of the rod, still further, a third embodiment of a method and apparatus for applying a polyethylene sleeve to a sinkerbar contemplates utilizing a hydraulic cylinder actuator for displacing the sleeve over a stationary rod or sinkerbar and wherein the sleeve is applied from a continuous roll of polyethylene tubing.
Those skilled in the art will further appreciate the above-mentioned advantages and features of the invention together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawing.